The present invention generally pertains to television systems and is particularly directed to improvements in extended-definition television (EDTV) systems.
An EDTV system provides extended definition video with a display having a wide-aspect ratio, such as 5:3 or 16:9, in contrast to the 4:3-aspect-ratio display produced from a standard NTSC television signal.
One method for achieving a compatible EDTV system is to utilize the "Fukinuki hole" which has been shown to exist in the NTSC spectrum, for transmitting additional video information required to provide a wide-aspect-ratio video display. The Fukinuki hole is described by Fukinuki, Hirano and Yoshigi, "Experiments on Proposed Extended-Definition TV with Full NTSC Compatibility", SMPTE Journal, pp. 923-929, October, 1984. In the standard NTSC signal the chrominance information occupies alternate quadrants C of a temporal-vertical-frequency domain, as shown in FIG. 1. The location of the luminance information in this domain is indicated by Y. The Fukinuki holes are the alternate quadrants F of such temporal-vertical-frequency domain that are above 2.0 MHz horizontal frequency and are not occupied by the chrominance information. In addition to a 131 cycles/picture height vertical offset and a 15 Hz temporal offset, a horizontal offset of at least 2 Mhz is desirable. The size and properties of the Fukinuki holes are therefore very similar to those of chrominance. The line-to-line and field-to-field phase relationships of both the chrominance information and the Fukinuki holes are shown in FIG. 2. In FIG. 2, FD indicates the fields, SL indicates the scan lines, .theta. indicates the phase of the chrominance information, .phi. indicates the phase of the Fukinuki holes.
If the additional video information required to provide a wide-aspect-ratio video display is encoded and modulated to provide augmentation signals that fit in the Fukinuki hole, then the presence of the augmentation signals would not be detected by existing standard NTSC receivers. At the same time, EDTV receivers would be able to extract the augmentation signals and process them to provide a wide-aspect-ratio video display.
An EDTV system that utilizes the Fukinuki hole for insertion of such augmentation signals is described in a report entitled "System Description, Advanced Compatible Television" submitted by the David Sarnoff Research Center, Inc. to the FCC Advisory Committee on Advanced Television Systems, Sept. 1, 1988. Such system is referred to herein as the "ACTV system". The ACTV system encodes a wide-aspect-ratio television signal having luminance information and chrominance information for transmission within a standard-television-signal-compatible interlaced format by dividing the television signal into center-panel segments from which the horizontally central portion of a television picture produced from said wide-aspect-ratio television signal is displayed in accordance with a standard-television-signal aspect ratio, and side panel segments from which the left and right side portions of the television picture produced from said wide-aspect-ratio television signal are displayed in accordance with the wide aspect ratio; arranging the center panel segments for transmission in the standard-television-signal-compatible format; producing augmentation signals from the side panel segments; and inserting the augmentation signals in the Fukinuki holes of the center panel segments.
The technique used to pack the augmentation signals in the Fukinuki holes is critical to the overall performance of both the old NTSC and the new EDTV receivers. Since some crosstalk is likely to exist between the augmentation signal that is transmitted in the Fukinuki hole and the existing luminance and chrominance signals, it is essential to encode the augmentation signals in a manner that minimizes perceptible inteference in existing NTSC receivers, and yet permits accurate separation and processing of the augmentation signals in new EDTV receivers.
The technique used in the ACTV system that enables the augmentation signals inserted in the Fukinuki holes to be separated from the center-panel luminance information is to group pixels into pairs spanning two adjacent lines in two adjacent fields, as shown in FIG. 13. If the augmentation signal in a Fukinuki hole (F), center-panel chrominance (C), and the component of center panel luminance exceeding 2 Mhz (Y), are each constrained to have the same values at the two different pixel locations, then it becomes possible to extract the augmentation signal F. This is because of a 180 degree phase shift that affects the Fukinuki hole subcarrier but not the color subcarrier. ##EQU1##
Separation of center-panel luminance information and chrominance information can then be performed by conventional line comb filtering or other prior art techniques.
In all cases, the degradation resulting from such errors as nonlinearities, differential phase, differential gain, sideband asymmetry, and channel noise should be minimized since they introduce residual errors and crosstalk effects.
Crosstalk from the augmentation signals to center-panel luminance information will produce the same dot structure as the crosstalk with center-panel luminance information originating from the chrominance information. The difference is that the dots will appear to crawl down the screen instead of up. An increase in horizontal or vertical frequency of the signals injected by the Fukinuki signal increases the horizontal or vertical size of the dots making them more visible and objectionable, while an increase in temporal frequency reduces the rate of crawl.
The dotted arrow in FIG. 1 shows that such increases in the vertical frequency content of the augmentation signal causes a decrease in the vertical frequency of the crosstalk signal imparted on the luminance channel, thereby making it more visible.
Crosstalk can also occur from the augmentation signals to the chrominance information, and in this case, existing comb filters will not be effective. In most cases, such crosstalk appears as a color flicker visible at low display spatial frequency. In theory, the average color produced by this flicker should be neutral. At high injection levels, however, some color may be visible due to nonlinearities during the conversion of I and Q chrominance components to the RGB phosphors of the cathode ray tube display. In addition, the visibility of color flicker increases as the vertical frequency or temporal frequency content of the augmentation signals increases, when the augmentation signals invade into the chrominance quadrants as shown by the dotted arrow emanating from the F region in FIG. 1.
In the ACTV system, the visibility of any crosstalk between the center-panel luminance information and the augmentation signal inserted in the Fukinuki holes will be greatly magnified in existing NTSC receivers due to the use of augmentation signals that are uncorrelated with either the luminance or chrominance information for the center panel. The crosstalk between the center-panel luminance information and the center chrominance information inserted in the alternate quadrants C of the temporal-vertical-frequency domain is not particularly noticeable in existing NTSC receivers because the center-panel chrominance information is correlated with the center-panel luminance information.
Consequently, the bandwidth of the augmentation signal must be minimized to insure that it does not exceed the boundaries of the Fukinuki hole, and the injection level must be reduced as much as possible. Unfortunately, as the injection level is reduced, the side panel signal-to-noise ratio S/N decreases and linearity of the new EDTV receivers becomes critical if crosstalk from the center panel to the side panels is to be prevented.
In the ACTV system, side-panel low spatial frequency components are horizontally compressed substantially so as to fit in a fixed narrow strip at the left and right picture edges. This results in two disadvantages: The first is the significant loss of signal-to-noise ratio (S/N), as compared to center panel S/N, causing a non-uniform and discernable "noise panel" effect in the EDTV display with a decrease in channel carrier-to-noise ratio. The second disadvantage of such side panel compression encoding of "horizontal lows" is that it imposes rigidity on the relative size of the left and right side panel. This would eliminate the use of "pan and scan" encoding which allows the operator to control by panning a center panel picture over a wider aspect ratio source picture. If the ACTV system were to attempt varying the relative size of the side panels, the center panel would appear to move from left to right in old standard aspect ratio television sets.
In the ACTV system, constraints are placed on temporal samples in successive video fields which are directed towards video sources at 30 frames per second. If, however, the video is derived from film in a 3-2 pulldown scheme, the method most common in North America, then motion artifacts due to the ACTV temporal constraints may result, since they are combined asynchronously with frame repetition film effects peculiar to the 3-2 pulldown process.
One object of the invention is to provide compatible side panel transmission with "Pan and Scan" capability by judicial use of the VBI and the Fukinuki hole.
A further object of the invention is to provide such side panel transmission with improved noise performance for FM and AM channels by facilitating higher injection levels of the "Fukinuki" signal by employing vertical expansion of side panel video information.
Yet another object of the invention is to provide motion error free transmission of such video signals derived from 24 frame per second film.
Still another object of the invention is to offer a better method for chrominance-luminance separation both for side panel and center panel video information.